gametophyte reduction

James W. Perry jperry at UWC.EDU
Mon Oct 4 16:30:26 EST 1999


Two theories to my recollection:

1. Homologous (transformation)
         Gpt primitive, spt. of secondary origin, a modified gpt - the gpt 
became "transfomed"

2. Antithetic (interpolation)

         Gpt of lower plants is of algal origin
         Delay in meiosis resulted in a spt present in Silurian plants
         Spt eventually became nutritionally independent
         Vegetative tissue arose from sterilization of sporogenous tissue

No observable evidence exists to my recollection.

Nothing quite like teaching causes one to ask questions. Maybe we should 
ask our students to do a little teaching if this is the result.

jim

At 03:12 PM 10/1/99 +0000, Dana Ann Dudle wrote:
>Hi All--
>
>After such helpful and interesting responses to my question regarding
>polyploidy, I have decided to try yet another question on y'all:
>
>What were the intermediate steps between the dominant, photosynthetic
>gametophyte and reduced sporophyte present in the non-vascular plants
>(bryophytes), and the dominant sporophyte that is present in all vascular
>plants (as far as I have been able to discern).  The oldest fossils of
>vascular plants that are most often referenced in textbooks and review
>articles, e.g. Cooksonia and Rhynia, are called sporophytes...
>
>IT seems as if this was a very important development in the evolution of
>plants, and yet I have found very little reference as to HOW this change
>occurred.  Does anyone know of fossil evidence or living transitional
>forms that may give some insight into this major change in the focus of
>the alternation- of- generations in land plants?
>
>I have always been taught that "mosses have dominant gametophytes, and
>ferns have dominant sporophytes", but I have not questioned the "how or
>why" until I started writing lectures and preparing classes on this topic.
>
>Any hints or leads would be greatly appreciated (as well as speculations!)
>
>Thanks,
>Dana
>*********************************
>Dana A. Dudle
>Dept. of Biological Sciences
>DePauw University
>Greencastle, IN  46135
>ddudle at depauw.edu
>*********************************


James. W. Perry, CEO/Campus Dean
Professor, Department of Biological Sciences
University of Wisconsin - Fox Valley
1478 Midway Road
Menasha, Wisconsin 54952-1297
Office: 920.832.2610
FAX: 920.832.2674
jperry at uwc.edu



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